NASA's TESS spacecraft discovers a new planet roughly the same size as Earth

The planet is located 100 light-years away from Earth and it could have liquid water on its surface.
Chris Young
An artist's impression of TOI 700 e.
An artist's impression of TOI 700 e.

NASA/JPL-Caltech / Robert Hurt 

NASA's Transiting Exoplanet Survey Satellite (TESS) spacecraft identified an Earth-sized world called TOI 700 e, located in its star's habitable zone.

Initial analysis shows the world is 95 percent Earth's size and it is likely a rocky planet, a report from NASA reveals. The discovery sheds new light on exoplanets that could harbor life, revealing new insight into the formation of our own solar system.

A new potentially habitable exoplanet

The habitable zone of a solar system is the region that is just the right distance from a star to allow liquid water to occur on a planet. Before the detection of the exoplanet TOI 700 e, astronomers had already discovered three planets in the same system, named TOI 700 b, c, and d. Planet d also orbits in its star's habitable zone.

"This is one of only a few systems with multiple, small, habitable-zone planets that we know of," said Emily Gilbert, a postdoctoral fellow at NASA’s Jet Propulsion Laboratory in Southern California and study lead. "That makes the TOI 700 system an exciting prospect for additional follow-up. Planet e is about 10% smaller than planet d, so the system also shows how additional TESS observations help us find smaller and smaller worlds."

Gilbert's team presented their findings in the journal The Astrophysical Journal Letters. Their paper details how TOI 700 is a small, cool M dwarf star located roughly 100 light-years from Earth in the southern constellation Dorado. Its relatively small size means its closest habitable planet, TOI 700 d, only has a 37-day orbit.

The search continues for alien life

NASA's TESS spacecraft trains its instruments on large areas of the sky for approximately 27 days at a time. This allows it to detect exoplanets via transits. Essentially, planets orbit within TESS's line of sight and slightly reduce the brightness of the light coming from their host star. This allows scientists to confirm the existence of an exoplanet and also deduce its orbital period based on the amount of time it dims its star's light.

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The scientists behind the discovery of TOI 700 e believe the exoplanet may be tidally locked, much like our moon. This means that one side of the planet constantly faces its host star. They will continue to analyze the TOI 700 system with space and ground-based observatories to gain new insight into planetary evolution.

Planets in the habitable zones of their host stars are of particular interest to scientists looking to better understand our own place in the universe. The Milky Way alone consists of approximately 400 billion stars. About 20 billion of these are sunlight stars. Estimates suggest that about a fifth of this sunlight, stars have an Earth-sized planet in their habitable zone.

These statistics are at the root of the Fermi Paradox, which famously asks why we haven't yet encountered intelligent alien life in any shape or form, given that there are so many planets located in a region of space that should be conducive to life.